1. Field of the Invention
The present invention relates to the separation of the palladium from the reaction medium resulting from the carbonylation of conjugated dienes with CO, in the presence of an alcohol, a halogenated hydracid and a palladium catalyst.
A principal advantage of the present invention resides in the fact that the palladium is separated in alcoholic solution and can be directly recycled for additional carbonylation catalysis, while at the same time retaining its activity.
2. Description of the Prior Art
It is known to this art, from Japanese Pat. No. 48.5564, to prepare monoesters of .beta.,.gamma.-unsaturated carboxylic acids by the carbonylation of conjugated dienes with carbon monoxide, in the presence of a monoalcohol, a non-halogenated palladium catalyst and a halogenated hydracid, at a temperature on the order of 100.degree. C. and under a carbon monoxide pressure on the order of 100 bars; the patent is silent regarding any method for recycling the palladium catalyst.
And U.S. Pat. No. 4,172,087 describes the synthesis of pent-3-enoic acid esters mixed with a large amount of nona-3,8-dienoic acid esters, by the carbonylation of butadiene with carbon monoxide, in the presence of an alcohol, a heterocyclic tertiary amine and a palladium halide complexed with a monodentate tertiary phosphine or a non-halogenated palladium salt complexed with a polydentate tertiary phosphine; the presence of a monodentate tertiary phosphine and a heterocyclic tertiary amine enables recovery of a liquid containing the palladium catalyst, after distillation of the pent-3-enoic acid esters and the nona-3,8-dienoic acid esters; the said liquid can be recycled into the medium to be carbonylated. A process of this type is carried out in the absence of halogenated hydracid; it displays a very low selectivitY in respect of pent-3-enoic acid esters.